1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having electrode extensions for current spreading.
2. Discussion of the Background
Gallium nitride (GaN)-based light emitting diodes (LEDs) have been used for is various applications, such as a natural color LED display, an LED traffic signal, a white LED, or the like. Also, a high-efficiency white LED is expected to replace a fluorescent lamp. In particular, the efficiency of the white LED reaches a similar level to the efficiency of the general fluorescent lamp.
The GaN-based light emitting diode is generally formed by growing epitaxial layers on a sapphire substrate, for example, and includes an N-type semiconductor layer, a P-type semiconductor layer, and an active layer interposed therebetween. Meanwhile, an N-electrode is formed on the N-type semiconductor layer and a P-electrode is formed on the P-type semiconductor layer. The electrodes of the light emitting diode are electrically connected to an external power supply, which drives the light emitting diode. Current flows into the N-electrode from the P-electrode via the semiconductor layers.
Generally, the P-type semiconductor layer has a high resistivity, and thus current may be unevenly spread in the P-type semiconductor layer and concentrated at a portion where the P-electrodes are formed, and current may also intensively flow through the edges of the diode. The current concentration leads to the reduction of a light emitting region, thereby degrading luminous efficiency. In order to improve current spreading, a transparent electrode layer having a low resistivity may be formed on the P-type semiconductor layer. Current that flows through the P-electrode is spread in the transparent electrode layer and then flows into the P-type semiconductor layer, thereby making it possible to expand the light emitting region of the light emitting diode.
However, since the transparent electrode layer absorbs light, the thickness thereof is limited. As a result, the transparent electrode layer has a limited current spreading ability. In particular, a large-area light emitting diode having a light-emitting region of about 1 mm2 or more, which is used for high output, has a limit to current spreading using the transparent electrode layer.
Meanwhile, the current flows through the semiconductor layers and then flows out to the N-electrode. Therefore, the current is concentrated on a portion of the N-type semiconductor layer, on which the N-electrode is formed, so that the current flowing in the semiconductor layer may be concentrated around a region where the N-electrode is formed.
FIG. 1 shows a light emitting diode having electrode extensions for current spreading according to the related art.
Referring to FIG. 1, the light emitting diode has a general rectangular shape, wherein n-electrode pads 21 and p-electrode pads 31 are disposed at edge portions to be opposite each other. Extensions 23 are formed along the edges of the light emitting diode from the n-electrode pads 21 and intrusion parts 25a and 25b extend inwardly from the extensions 23 of the edges. The intrusion parts 25a and 25b intrude into the light emitting diode in parallel with an imaginary diagonal line extending from one of the four corners of the light emitting diode.
Meanwhile, intrusion parts 35a each extend in a diagonal direction from the p-electrode pads 31, and sub-intrusion parts 35b extend by being branched from the intrusion parts 35a. 
A transparent electrode layer 39 is disposed on the upper surface of the light emitting diode. The intrusion parts 35a and the sub-intrusion parts 35b are disposed on the transparent electrode layer 39 to assist in current spreading.
Although not shown in FIG. 1, the light emitting diode includes an n-type lower semiconductor layer, a p-type upper semiconductor layer, and an active layer, in which the transparent electrode layer 39 is disposed on the p-type upper semiconductor layer. In addition, the n-electrode pads 21, the extensions 23, and the intrusion parts 25a and 25b are disposed on the n-type lower semiconductor layer and the p-type electrode pads 31 are disposed on the p-type upper semiconductor layer or the transparent electrode layer 39.
The related art adopts the extensions 23 and the intrusion parts 25a and 25b to assist in current spreading on the n-type lower semiconductor layer and also disposes the intrusion parts 35a and the sub-intrusion parts 35b to assist in current spreading on the transparent electrode layer 39.
However, the related art removes a relatively wide area of the active layer and the upper semiconductor layer in order to form the extensions 23. Therefore, the light emitting area is considerably reduced and the light output is reduced accordingly. In addition, the intrusion parts 25a and 25b and the intrusion parts 35a and 35b are disposed in a rotational symmetry type based at the center of the light emitting diode in order to evenly emit light over the entire region of the light emitting diode. However, light may not be evenly emitted over the entire region of the light emitting diode, and in particular, light may be unevenly emitted at the central region of the light emitting diode.